Xiaomi TV (MiTV) has a Black Screen

27 Oct 2018
# MiTV black screen,  faulty LED panel    
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This is a common complaint in MiTV and also in other makes.  Some of these black screen faults are caused by OS updates;  others are due to hardware component failures.  The Power Supply Board is usually the culprit.  This article intends to serve as a guide to troubleshoot this black screen problem, using MiTV4 as example.

How MiTV works?

MiTV has only a 3 components;  the Main Board (MB）,  the Power Supply Board （PSB）and the Logic Display Board (LDB) or commonly known as T-Con board.  The LDB  Board is usually shielded inside a metal cover.   Behind the plastic and metal covers,  there are also other components such as Bluetooth receiver,  the speaker modules and most important of all,  the LED backlights.   The following shows the layout and back panel of MiTV4;  other models of MiTV are quite similar

The MB  of MiTV4 contains the CPU,  I/O devices and the interfacing components to work with the LDB to light up the LED  panel.  The PSB will supply  12V  power lines to the MB which will do all the necessary startup and "instruct" the LDB, the indicators and the remote controls to work with the LED panel. The PSB also supplies the 96 Volt supply to power the LED backlights.

What can go wrong?

When there is black screen,  it will involve faults in the PSB,  MB and the also the LDB.  If these component boards are healthy,  then the fault could lie in the LED panel,  meaning the interfacing board within the LED panel might be faulty.  When this happen,  the repair will be complex.  Our 55" MiTV4 had a  LED panel fault and was replaced during the 1 year warranty period.

How to detect what went wrong?

The traditional wisdom is to shine a bright torch light as close as possible at the screen and at an angle  to determine if there are moving images on the screen.   In here,  the torch light is simulating the backlight to check if the faulty backlight is the cause.

The following suggestions should help to troubleshoot the faults.

Description	Possible causes and actions	Remark (Dbclick to enlarge video/pictures)
I)  No Moving Image and No Sound
1.  Power Indicating lights not on	1)  Make sure the power is plugged in and the remote control’s battery is good by replacing the battery 2)  If still not working,  press the white start button underneath and at the centre of the TV	Reference video found in YouTube for information (Click here for full screen)
2.  Indicating lights are on	Try to factory reset the OS by pressing the [Confirm] and the [Restore] at the same time and start the TV by pressing the white start button after powering off  the  TV for about 20 seconds	(Click here for more information on how to do a factory reset).
3)  The screen is still in complete darkness	If the TV has been synchronized before for screen mirroring,  use the hand phone to check if it can locate  the address to the TV	If cannot locate the address of the TV,   most likely the TV is dead with faulty MB or PSB
4)  The screen is back		This screen will be shown on successful factory reset.
II)  Got Moving images and got sound
	Suspect PSB has problem supplying power for the backlights Most likely the LED backlights are faulty.	Reference video found in YouTube for information (Click here for full screen)
III)  No moving images but got sound
	Check the supply voltages to the LDB and PSB.   Most likely a)  The LDB is faulty or the LCD screen is faulty b)  The PSB is faulty

Flow Chart for the Repair

(Double click flow chart for full screen)

Why the Power Supply Board  (PSB) can be Faulty?

The Power Supply Board  supplies not only power to the MB but also the power to the LED backlight directly.  When instructed by the MB,  a high voltage (96 volts for 55" MiTV4) will be sent to the  LED backlight to light up the screen.  If there is a faulty LED,  this 96 Volt power rail will be short circuited  and this may damage the PSB.  The LED strip's  PCB rail could be  burnt off,  resulting power  not being supplied to a strip of  LEDs as shown in the following picture.

How To Repair the LED Backlights?

There is no repair video yet for repairing the backlight of MiTV4 series.  In particular,  the MiTV4 has a 9 mm thick LED panel,  requiring Edge LED or ELED type of  backlights  to be installed at the bottom of the LED screen instead of installing it directly behind and underneath the LED panel (Direct LED or DLED)..  Because of this,  many users of MiTV have complained about the heat generated by the backlights at the bottom of TV.   

However,  here is good video about how to replace and test the LED backlights for common and traditional type of  TVs with DLED.  This could apply to other MiTV4 series such as MiTV4A etc

Usually,  users were able to repair most TV problems by first replacing the power supply board,  then follow by the Main board or logic display board in that sequence.  

How to Prolong the life of LED backlights?

Users have been advised to lower the brightness of the TV to about 50%  to 75% so as to reduce the heat caused by the LEDs backlights.   Having proper ventilation at the location where LED backlight is located will prolong its life. 

Where can we buy the MiTV Spares?

MiTV spares are often offered for sale in TaoBao as the vendors stripped old broken TV set to salvage the parts.  They would usually test the boards and give 90 days warranty or money back if the board can be returned within 7 days.   However,  it is always good to ensure that one would not be cheated when buying stuff from TaoBao. 
If one cannot find the spares in TaoBao,  it may be because the MiTV is quite new and one might have to wait for a while.

The Boards of 55" MiTV4

The following pictures are taken from a 55" MiTV4 .  When ordering the part,  give the vendors the correct  parts number copied directly from your TV.  

The Main Board	The Power Supply Board	The Logic Display Board (Different for different panel makers)
The remote Control Board	LED strips w/o alum panel	LED strips inside alum panel
Speakers and Remote control

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